The invention relates to a process in which hydrocarbons and steam produced by a gas conversion process are used to stimulate bitumen production and transport. More particularly, the invention relates to a process in which natural gas is converted to a Fischer-Tropsch synthesis gas feed, from which liquid hydrocarbons and steam are produced to facilitate bitumen production and transportation by pipeline to refining facilities.
Very heavy crude oil deposits, such as the tar sand formations found in places like Canada and Venezuela, contain trillions of barrels of a very heavy, viscous petroleum, commonly referred to as bitumen. The bitumen has an API gravity typically in the range of from 5O to 10O and a viscosity, at formation temperatures and pressures, that may be as high as a million centipoise. The hydrocarbonaceous molecules making up the bitumen are low in hydrogen and have a resin plus asphaltenes content as high as 70%. This makes the bitumen difficult to produce, transport and upgrade. Its viscosity must be reduced in-situ underground for it to be pumped out (produced). While in-situ bitumen dilution with an aromatic solvent has been proposed for the viscosity reduction (Canadian patent 1,034,485), bitumen production is commonly facilitated by steam stimulation. In steam stimulated bitumen production, hot steam is injected down into the formation to lower the viscosity of the oil sufficient to pump it out of the ground. This is disclosed, for example, in U.S. Pat. No. 4,607,699. U.S. Pat. No. 4,874,043 discloses alternately pumping steam and hot water into the ground. However, steam-produced bitumen is still too viscous to be transported to upgrading facilities by pipeline. Therefore, it must be diluted with a compatible, lower viscosity liquid, in an amount sufficient to produce a mixture having a viscosity low enough to be transported by pipeline. This is known and disclosed, for example, in U.S. Pat. No. 6,096,192. One significant feature of bitumen production is a source of readily available steam, some of which is lost or consumed in the process and cannot be recovered. Another is a plentiful supply of a compatible bitumen diluent, especially if it is used in a once-through fashion and preferably without requiring a downstream bitumen conversion operation to produce the diluent. In the ""192 process, the diluent is obtained by forming a mixture of natural gas condensate and low boiling hydrocarbons obtained from partial catalytic hydroconversion of the bitumen. A plentiful source of hydrogen is required for upgrading bitumen middle distillate fuels produced by the bitumen conversion. When bitumen diesel production is desired, a blending component relatively high in cetane is needed to mix with the lower cetane bitumen diesel.
Gas conversion processes produce hydrocarbons from a synthesis gas derived from natural gas, as is well known. The synthesis gas comprises a mixture of H2 and CO, which are reacted in the presence of a Fischer-Tropsch catalyst to form hydrocarbons. Fixed bed, fluid bed and slurry hydrocarbon synthesis processes have been used, all of which are well documented in various technical articles and in patents. Both light and heavy hydrocarbons are synthesized. In addition to hydrocarbon production, these processes also produce steam and water. It would be an improvement to the art if bitumen production and gas conversion could be integrated, to utilize features of the gas conversion process to enhance bitumen production and products.
The invention relates to a process in which natural gas is converted to a synthesis gas feed, from which liquid hydrocarbons and steam are produced to facilitate bitumen production, and transportation by pipeline to refining facilities. The conversion of natural gas to synthesis gas and the production of hydrocarbons from the synthesis gas will hereinafter be referred to as xe2x80x9cgas conversionxe2x80x9d. The natural gas used to produce the synthesis gas will typically and preferably come from the bitumen field or a nearby gas well. The gas conversion produces liquid hydrocarbons, steam and water. Thus, the invention broadly relates to an integrated gas conversion and bitumen production process, in which gas conversion steam and hydrocarbon liquids are respectively used to stimulate bitumen production and dilution for transport. The conversion of natural gas to a synthesis gas is achieved by any suitable synthesis gas process. The synthesis gas comprises a mixture of H2 and CO and is contacted with a suitable hydrocarbon synthesis catalyst, at reaction conditions effective for the H2 and CO in the gas to react and produce hydrocarbons, at least a portion of which are liquid. A portion of these liquid hydrocarbons, preferably lower boiling hydrocarbons and more preferably comprising a naphtha fraction, are used to dilute the viscosity of the bitumen produced by the process, so that it can be transported to a refining facility by pipeline. The gas conversion process also produces high and medium pressure steam, all or a portion of which are injected into the ground to stimulate the bitumen production. In addition to hydrocarbons, water is produced by the hydrocarbon synthesis reaction, all or a portion of which may be heated to produce steam for the bitumen production. Thus, by xe2x80x9cgas conversion steamxe2x80x9d or xe2x80x9csteam obtained or derived from a gas conversion processxe2x80x9d in the context of the invention is meant to include any or all of the (i) high and medium pressure steam produced by the gas conversion process and (ii) steam produced from heating the hydrocarbon synthesis reaction water, and any combination thereof. This is explained in detail below. By bitumen production is meant steam stimulated bitumen production, in which steam is injected into a bitumen formation, to soften the bitumen and reduce its viscosity, so that it can be pumped out of the ground.
While the hydrocarbon diluent may be recovered, and reused or recycled for the bitumen dilution, it will be more efficacious if is used on a once-through basis, to avoid having to pipeline it from the downstream bitumen conversion facility, back to the bitumen dilution operation. Thus, in a preferred embodiment, the hydrocarbon diluent is not recycled, but is used on a once-through basis. In another embodiment, it is recovered at the bitumen refining facility and recycled back to the bitumen production facility, where it is again used to dilute the bitumen for the pipeline transportation. In a typical integrated process of the invention, a portion of the hydrocarbons synthesized by the gas conversion process are upgraded to produce a synthetic crude or more useful lower boiling products. The bitumen is also upgraded. Upgrading comprises fractionation and typically and preferably one or more conversion operations. By conversion is meant at least one operation in which at least a portion of the molecules is changed and which may or may not include hydrogen as a reactant. For the bitumen this includes conversion by cracking, which may be non-catalytic coking or catalytic cracking, followed by one or more hydroconversion operations explained in more detail below. In another embodiment of the invention, the gas conversion portion of the process can be adjusted to produce extra hydrogen useful for converting the bitumen, lower boiling hydrocarbons produced by the bitumen upgrading and/or hydrocarbons synthesized by the gas conversion process. The hydrocarbon synthesis produces a tail gas that contains methane and unreacted hydrogen. In a further embodiment, this tail gas may be used as fuel to produce steam for bitumen production, pumps or other process utilities.
In a broad sense, the integrated gas conversion and bitumen production process of the invention comprises (i) stimulating the production of bitumen with steam obtained from a natural gas fed gas conversion process that produces steam and hydrocarbons, including liquid hydrocarbons and, (ii) diluting the produced bitumen with a diluent comprising at least a portion of the liquid hydrocarbons to form a pipelineable fluid mixture comprising the bitumen and diluent, and (iii) transporting the mixture by pipeline to a bitumen upgrading facility. By liquid hydrocarbons is meant hydrocarbons that are liquid at standard conditions of room temperature and pressure. In further embodiments the process includes upgrading at least one of, and preferably both the bitumen and at least a portion of the gas conversion hydrocarbons. In a still further embodiment, which is a preferred embodiment, the diluent will comprise a naphtha fraction. In yet further embodiments, at least part of any hydrogen required for upgrading will be produced from the synthesis gas. In a more detailed embodiment, the invention comprises the steps of (i) converting natural gas to a synthesis gas, (ii) producing liquid hydrocarbons and steam from the synthesis gas, (iii) using a portion of the steam to produce bitumen, and (iv) using a portion of the liquid hydrocarbons to dilute the bitumen to lower its viscosity sufficient to enable it to be transported to a refining facility by pipeline. In a still more detailed embodiment the process of the invention comprises:
(i) converting natural gas to a hot synthesis gas comprising a mixture of H2 and CO which is cooled by indirect heat exchange with water to produce steam;
(ii) contacting the synthesis gas with a hydrocarbon synthesis catalyst in a hydrocarbon synthesis reactor, at reaction conditions effective for the H2 and CO in the gas to react and produce heat, liquid hydrocarbons and a gas comprising methane and water vapor;
(iii) removing heat from the hydrocarbon synthesis reactor by indirect heat exchange with water to produce steam;
(iv) passing at least a portion of the steam produced in either or both steps (i) and (iii) down into a tar sand formation to heat soak and reduce the viscosity of the bitumen, sufficient for it to be removed from the formation;
(v) producing the bitumen by removing it from the formation;
(vi) reducing the viscosity of the produced bitumen by mixing it with a diluent comprising a portion of the liquid hydrocarbons produced in step (ii), and
(vii) transporting the mixture by pipeline to a bitumen upgrading facility.
Further embodiments include those set forth above, as well as cooling the gas and water vapor produced in step (ii) to condense out and separate the water and form a methane-containing tail gas reduced in H2O, with the water optionally used for the generation of additional steam and the tail gas used as fuel. The gas fuel is used for generating steam for bitumen production and associated process utilities.